Thiourethane resins are resins having a thiourethane group that are formed by reacting a thiol group of a thiol compound having at least two thiol groups in a molecule thereof, and an isocyanate group of an isocyanate compound having at least two isocyanate groups in a molecule thereof.
The following lists examples of the characteristics of thiourethane resins.                Thiourethane resins are used in a wide range of applications such as adhesives, coating agents or the matrix of fiber-reinforced composite materials since they have properties resembling those of urethane resins and have superior toughness, impact resistance and abrasion resistance.        Thiourethane resins are also used in optical substrates due to their high refractive index (Patent Document 1).        The reaction between a thiol group of a thiol compound and an isocyanate group of an isocyanate compound proceeds rapidly due to the presence of a catalyst such as a basic compound or phosphine compound (Patent Document 2). Consequently, it is not necessary to use a tin-based catalyst, for which there are concerns over toxicity, used in the production of urethane resins.        
The thiol compound and isocyanate compound serving as raw materials of thiourethane resins are frequently used as two-component curable compositions. A cured product in the form of the thiourethane resin is obtained by mixing a composition containing a thiol compound and a composition containing an isocyanate compound in the presence of a catalyst. From the viewpoint of handling ease of the two-component curable composition, the duration of pot life until gelling begins after having mixed the two compositions is preferably long to a certain degree. However, if the amount of catalyst is reduced in order to extend pot life, there is the problem of the curing time from the time gelling begins until a certain hardness is reached also becoming long.
A method has been proposed for realizing both short curing time and long pot life that consists of reacting a thiol group of a thiol compound with an isocyanate group of an isocyanate compound using a co-catalyst composed of a phosphine compound, Michael acceptor and methanesulfonic acid (Non-Patent Document 1).
This publication indicates that the use of this co-catalyst allows the obtaining of a pot life of several minutes to 13 minutes.